CAIRO (AP) — Protesters flooded Cairo’s Tahrir Square on Friday in the second giant rally this week, angrily vowing to bring down a draft constitution approved by allies of President Mohammed Morsi, as Egypt appeared headed toward a volatile confrontation between the opposition and ruling Islamists.

The protests have highlighted an increasingly cohesive opposition leadership of prominent liberal and secular politicians trying to direct public anger against Morsi and the Islamists — a contrast to the leaderless youth uprising last year which toppled autocrat Hosni Mubarak.

The opposition announced plans for an intensified street campaign of protests and civil disobedience and even a possible march on Morsi’s presidential palace to prevent him from calling a nationwide referendum on the draft, which it must pass to come into effect. Top judges announced Friday they may refuse to monitor any referendum, rendering it invalid.

If a referendum is called, “we will go to him at the palace and topple him,” insisted one protester, Yasser Said, a businessman who said he voted for Morsi in last summer’s presidential election.

Islamists, however, are gearing up as well.

The Muslim Brotherhood, from which Morsi hails, drummed up supporters for its own mass rally Saturday. Islamists boasted their turnout would show that the public supports the push by the country’s first freely elected president to quickly bring a constitution and provide stability after nearly two years of turmoil.

Brotherhood activists in several cities passed out fliers calling for people to come out and “support Islamic law.” A number of Muslim clerics in Friday sermons in the southern city of Assiut called the president’s opponents “enemies of God and Islam.”

The week-old crisis has already seen clashes between the two camps that left two dead and hundreds injured. On Friday, Morsi opponents and supporters rained stones and firebombs on each other in the Mediterranean city of Alexandria and the southern city of Luxor.

The Islamist-led assembly that worked on the draft for months passed it in a rushed, 16-hour session that lasted until sunrise Friday.

The vote was abruptly moved up to pass the draft before Egypt’s Constitutional Court rules on Sunday whether to dissolve the assembly. Liberal, secular and Christian members and secular members had already quit the council to protest what they call Islamists’ hijacking of the process.

The draft is to be sent to Morsi on Saturday to decide on a date for a referendum, possibly in mid-December.

The draft has a distinctive Islamic bent — enough to worry many that civil liberties could be restricted, though its provisions for enforcing Shariah, or Islamic law, are not as firm as ultraconservatives wished.

Protests were first sparked when Morsi last week issued decrees granting himself sweeping powers that neutralized the judiciary. Morsi said the move was needed to stop the courts — where anti-Islamist or Mubarak-era judges hold many powerful posts — from dissolving the assembly and further delaying Egypt’s transition.

Opponents, however, accused Morsi of grabbing near-dictatorial powers by sidelining the one branch of government he doesn’t control.

Anger at Morsi even spilled over into a mosque where the Islamist president joined weekly Friday prayers. In his sermon, the mosque’s preacher compared Morsi to Islam’s Prophet Muhammad, saying the prophet had enjoyed far-reaching powers as leader, giving a precedent for the same to happen now.

“No to tyranny!” congregants chanted. Morsi took to the podium and told the worshippers that he too objected to the language of the sheik and that one-man rule contradicts Islam.

Friday’s crowd in Tahrir appeared comparable in size to the more than 200,000 anti-Morsi protesters who thronged the central plaza three days earlier. Tens of thousands more marched Friday in Alexandria and other cities.

The atmosphere was festive, with fireworks going off and banners stretched over the crowd. One showed a popular pop star singing in a cartoon bubble, “Your constitution is void.” More tents sprung up in the plaza’s central traffic circle, as protesters sought to increase their week-old sit-in.

Large marches from around Cairo flowed into the square, chanting “Constitution: Void!” and “The people want to bring down the regime.”

Figures from a new leadership coalition took the stage to address the crowds. The coalition, known as the National Salvation Front, includes prominent democracy advocate Nobel Peace laureate Mohamed ElBaradei, leftist Hamdeen Sabbahi and former Arab League chief Amr Moussa.

“We are determined to continue with all peaceful means, whatever it takes to defend our legitimate rights,” ElBaradei told the crowd. He later posted on Twitter that Morsi and his allies are “staging a coup against democracy” and that the regime’s legitimacy “is eroding.”

Sabbahi vowed protests would go on until “we topple the constitution.”

“The revolution is back ... We shall be victorious,” said Sabbahi, who came in a surprisingly close third in the presidential election.

The coalition is aiming to rally together the disparate opposition factions, hoping to focus a movement that critics say failed to capitalize on its gains after Mubarak’s fall. That they appear to have won a degree of acceptance among protesters is a significant shift, since mainstream liberal politicians were dismissed by many activists as out of touch, disorganized and out for their own interests.

ElBaradei’s strong move to the fore is particularly notable. He was an inspiration for some of the youth in the 2011 anti-Mubarak uprising, but long appeared reluctant to play a leadership role and was criticized as remote and elitist.

The politicians still lack grassroots, warned Manal Tibe, a rights activist who was the first member of the constitutional assembly to withdraw in protest against the Islamists.

The street “is moving faster than the political opposition leaders,” and some protesters worry they won’t push strong enough demands, she said.

Protester Mohammed Taher, a 45-year-old computer engineer, said the rallies have been fueled by widespread outrage, not politicians’ organizing. “People came here without a rallying machine,” he said.

If the charter does go to a referendum, the politicians do not have the public reach or enough time to galvanize a “no” vote, she said.

The opposition also is counting on a revolt by the judiciary. Many judges have gone on strike, raising the possibility they would not serve as election monitors as required. Two top judicial bodies, the High Administrative Court and the State Council, said they would confer with the main Judges’ Association on whether to monitor.

The Salvation Front warned on Friday that holding a referendum would “deal a deadly blow to the legitimacy of the president.”

But if a referendum is held, the opposition faces the tough choice of whether to boycott — and risk sidelining itself — or trying to rally a “no” vote — and risk losing in the face of Islamists’ powerful grassroots electoral machine.

The Brotherhood and harder-line Islamists won nearly 75 percent of the seats in last winter’s parliament election. The Brotherhood’s Morsi, however, won only about 25 percent in a first-round presidential vote and just over 50 percent in the runoff.

Safwat Hegazy, a hardline cleric allied to the Brotherhood, challenged the opposition in a Tweet to “go to the people in the referendum ... If the people are by your side and say no, we’ll know who you are and who we are.”

The opposition has been emboldened by the anger at the Brotherhood’s rule after Morsi’s edicts ignited criticism brewing for months that the group has used election victories to monopolize power in Egypt.

Many at Friday’s protest mocked the constitutional assembly session, after watching it all night on television. During the marathon gathering, the 85 remaining members of the 100-member body voted on each of the more than 230 articles, passing all by wide margins.

The assembly’s white-bearded president, Hossam al-Ghiryani, kept the voting at a rapid clip, badgering members to drop disputes and objections and move on.

At times the process appeared slap-dash, with fixes to missing phrasing and even several entirely new articles proposed, written and voted on in the wee hours of night.